JPH05308026A - Manufacture of rotary transformer - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a cylindrical rotary transformer for communicating signals with a rotating magnetic head by which the coil winding yield can be improved and the manufacturing cost can be reduced. CONSTITUTION:After an outer shape mold is put on an inner shape mold composed of a metallic mold 3 for forming vertical grooves and metallic mold 4 for forming horizontal grooves provided with a plurality of slit-like recessed grooves on the peripheral surfaces of projected lines 4b and compression forming magnetic powder put between the metallic molds, an outer core is obtained by heat-treating the formed body at a high temperature and a rotary transformer is formed by incorporating an inside core in the outside core. Since the grooves for winding coils are not formed by machining, but formed at the time of forming the outside core, the manufacturing cost of the title transformer can be reduced and, since slit-like projecting sections are provided at the bottom of horizontal grooves as guides for winding coils, the coils can be wound accurately and the coil winding yield can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a rotary transformer used for transmitting / receiving a signal to / from a rotating magnetic head such as a video tape recorder or a digital audio tape recorder.

[0002]

2. Description of the Related Art There are two types of rotary transformers used in magnetic recording / reproducing devices such as video tape recorders and digital audio tape recorders, disk type and cylindrical type. ， The use of cylindrical rotary transformers has increased due to the increase in the number of channels and the increase in density required as the number of functions has increased. The structure of this rotary transformer is such that both the inner core made of a cylindrical ferrite and the outer core made of ferrite are coaxially opposed to each other with a certain minimum gap maintained, and they are required on each of the facing surfaces. A horizontal groove for a coil having the number of channels is provided, and the coil is mounted in the horizontal groove for the coil. In addition, a lateral groove for fitting a short ring is provided between each channel of the inner core.

A conventional ferrite core for a cylindrical rotary transformer is usually manufactured as follows.

First, as shown in the manufacturing process diagram of FIG.
A cylindrical ferrite sintered body is produced and then finished by special machining to obtain the desired dimensional accuracy.As a method for producing the ferrite sintered body, the raw material with the desired composition in the figure is used. After mixing and mixing, it is calcined at a temperature of 1000 ° C or lower. Next, this calcinated product is pulverized, and an appropriate amount of a binder such as an aqueous solution of polyvinyl alcohol (PVA) is added to the pulverized powder for granulation, and then the granulated powder is uniaxially compression molded by a cylindrical mold. The cylindrical molded body thus obtained is subjected to main firing at a high temperature of 1000 ° C. or higher to obtain a cylindrical ferrite sintered body, or the above ferrite calcined pulverized powder is kneaded with a resin and transfer molded into a cylindrical shape. 1000 ℃ after the heat treatment process for degreasing
There are two methods of obtaining the same ferrite sintered body by performing the above high temperature main firing (for example, JP-A-61-84).
(See Japanese Patent Publication No. 006).

However, the ferrite sintered body obtained by either of the above methods should avoid insufficient pressure transmission in the central portion of the molded body in the case of uniaxial molding when manufacturing the molded body before firing. As shown in the perspective view of FIG. 16 showing the warp and shrinkage due to the firing of the formed body due to the non-uniformity of the forming density, the ferrite sintered body 32 is warped in the central portion, and the formed body 33 is warped. Since it is accompanied by a large shrinkage of 10% or more in comparison with the size, it is very difficult to keep the size and accuracy within the strict required specifications as a rotary transformer core.

Therefore, for example, when a cylindrical core is manufactured, it is usually performed as follows. First, prepare a cylindrical ferrite sintered body with an inner and outer diameter of about 1 mm or more larger than the desired size, and perform the primary grinding of the outer peripheral surface of this ferrite sintered body with a centerless grinder. Roughly grind the inner peripheral surface with an inner surface grinding machine based on the surface, then both the inner and outer peripheral surfaces are surface-finished with a special grinding machine, and then lateral grooves for coils of the required number of channels are grooved along the inner or outer circumference. Alternatively, simultaneous groove processing is performed with a rotary continuous blade to obtain dimensional accuracy as a final product of a cylindrical rotary transformer core.

In this case, the parts that require particularly high precision are the relative gap size of the two cylindrical cores and the shape and dimensional accuracy of the coil lateral groove. The lateral groove shape is also as shown in the schematic diagram of the coil winding state in FIG. In addition, if the radius of curvature of the groove side taper portion 34 and the groove bottom corner portion 35 is large, and more than several hundred cores 36 are machined with the same groove grinding wheel, it will be constant due to changes with time due to wear of the grinding blade. At present, it is difficult to obtain a groove shape having a size. As for the number of man-hours, the ratio of groove processing is the highest. next,
The coil 37 is wound in the coil groove. Here, the coil 37 can be mounted by forming the coil 37 by directly winding the coated copper wire in the coil groove of the inner and outer cores, or particularly by using the outer core. In this case, a method of inserting a preliminarily prepared air core coil is used. In this way, the inner core and the outer core are assembled into a finished rotary transformer.

[0008]

As described above, in the cylindrical rotary transformer core according to the conventional method, it is inevitable that the ferrite sintered body is significantly shrunk and the warp of the central portion is reduced, and the shrinkage amount is allowed in advance to allow a sufficient margin. A cylindrical ferrite sintered body with a size is produced, and finally the desired dimensions and accuracy are obtained by precision processing from rough grinding, and further groove processing for coil mounting is performed to finish the ferrite core for rotary transformer. .. However, this method has a large process man-hour including groove machining, and the material is hard, resulting in poor process yields such as cracks and chips during machining. Since the taper and radius of curvature of the groove bottom corner increase with the number of processed pieces, it is difficult to obtain a groove shape with a certain size, so when the coil is formed that requires more aligned winding, the coil may come off or float, There has been a big problem that it causes a decrease in wire yield and it is difficult to manufacture a rotary transformer at low cost. Furthermore, in the conventional method, there is no method of forming the groove on the inner peripheral surface of the outer core by molding,
Grooving was the only method of machining.

The present invention solves the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a method of manufacturing a cylindrical rotary transformer at a low cost, in which the winding yield is dramatically improved.

[0010]

In order to achieve this object, the present invention provides a peripheral surface around a vertical groove forming die having a vertical groove forming piece protruding in a radial direction on at least a part of a central axis. A plurality of lateral groove forming dies having a plurality of ridges having a plurality of slit-shaped grooves on the peripheral surface are arranged and combined to form an inner die, and a cylindrical outer die is formed on the outer periphery of the inner die. Cover the mold,
A desired amount of magnetic powder was filled between the outer mold and the inner mold, and a pressing mold was further inserted between the inner mold and the outer mold to compression-mold the magnetic powder. After that, the lateral groove forming die is moved in the central axis direction to extract the molded body, and the molded body is subjected to high temperature treatment to form a cylindrical outer core, and the slit-shaped convex portion formed on the inner peripheral surface of the outer core is formed. This is a method for manufacturing a rotary transformer in which an outer coil is installed in the lateral groove that is provided and then an inner core in which an inner coil is formed in a lateral groove on the outer peripheral surface is installed in the outer core.

[0011]

According to the above-mentioned manufacturing method, the groove formation on the inner peripheral surface of the cylindrical core is machined due to the warp during firing due to the nonuniformity of the molding density, which is inevitable in the conventional method, and the deformation accompanying the large shrinkage. Different from the method used in, the cylindrical outer core and inner core are manufactured by the realization of a uniform molded body and die molding, which eliminates the groove processing step that has been performed up to now. Since there is a slit-shaped convex portion as a winding guide, it is possible to obtain an inexpensive one with a much higher winding yield than the conventional one.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a manufacturing process diagram of a rotary transformer in one embodiment of the present invention. As an example of a method for manufacturing a core for a rotary transformer, as shown in an exploded perspective view of an inner die used in the molding step of FIG. Around the vertical groove forming die 3 having the vertical groove forming piece 2,
A ridge 4b divided into four and having a slit-shaped groove 4c shown in an enlarged perspective view of a lateral groove forming die of FIG. 2 for forming a lateral groove having tapered portions 4a at both ends has a desired number of channels. The lateral groove forming die 4 provided only on the periphery of the vertical groove forming die 3 is fixed to the periphery of the vertical groove forming die 3 by the caps 5 and 6 having a taper on the inner cylindrical portion. The mold 7 is obtained. Next, as shown in the perspective view of FIG. 5, after inserting the inner mold 7 into the downward pressing die 8, as shown in the perspective view of FIG. 9, and a desired amount of magnetic powder 10 is uniformly filled between the outer shape die 9 and the inner shape die 7 with a powder supply nozzle 11 or the like. The lower pressing mold 8 and the upper pressing mold 12 are inserted into and compression molded.

Next, as shown in the partially cutaway perspective view of FIG.
After removing the caps 5 and 6 for fixing the four lateral groove forming molds 4, the vertical groove forming mold 3 is extracted. In addition, 13 shown in the figure is a molded body of the magnetic powder 10.

Next, as shown in the partially cutaway perspective view of FIG.
Center bar 14 having screw parts at the upper and lower ends which are opposite to each other
Is inserted into the space from which the vertical groove forming mold 3 has been removed, and the upper and lower end screw parts have a taper on the inner cylindrical part 15,
16 is screwed in from the vertical direction to just before the taper portions 4a of the four lateral groove forming dies 4. Then, as shown in the partially cutaway perspective view of FIG. 9, the center rod 14 is rotated in a direction in which the cutting dies 15 and 16 approach each other.
By moving 16 at the same speed and utilizing the mutual taper of the punching dies 15 and 16 and the lateral groove forming die 4, the four lateral groove forming dies 4 are moved in the central axis direction to form the molded body 13.
Then, as shown in the partially cut-away perspective view of FIG. 10, the molded body 13 is extracted from the outer shape die 9 by the die 17.

At this time, the order of taking out the molded body 13 is not limited to this example. First, the molded body 13 is removed from the outer shape mold 9 and then the vertical groove forming mold 3 of the inner mold 7 is extracted.
The lateral groove forming die 4 may be moved in the central axis direction and withdrawn from the forming body 13 as described above.

Next, the molded body 13 thus obtained is subjected to a high temperature treatment to form a cylindrical core, and as shown in the sectional view of the rotary transformer of FIG. Outer coil 1 with built-in coil in lateral groove
In the inner core 20, a coil is wound around a lateral groove on the outer peripheral surface of the inner core 20 to form an inner coil 21, and a short ring 22 is formed. The short ring 22 is incorporated into the outer coil 19 to produce a rotary transformer. Of.

Here, an example in which the number of vertical grooves is four has been described, but the number of vertical grooves is not limited to this, and basically, a vertical groove forming die having two or more vertical grooves and its equivalent. It suffices that it has a configuration in which the lateral groove forming dies divided into the above number are combined.

Although the desired amount of magnetic powder to be filled is used in a powder state, the preformed product may be used by preforming it into a shape that can be easily put into the mold.

The magnetic powder may be a provisional calcined product of ferrite, a mixture of highly crystalline ferrite magnetic powder which has been sufficiently ferritized by high temperature sintering and glass powder, or a mixture of these and a resin.

Further, in the case of the compression molding, in the case of the mixture of the above-mentioned glass powder or resin, it can be carried out in a heated state at a temperature at which the glass powder or resin is melted. The resin can be either thermosetting or thermoplastic.

Specific examples will be described below. (Example 1) As shown in FIG. 3, firstly Fe ₂ O ₃ 48m
ol%, NiO 15mol%, ZnO 34mol
%, CuO 3 mol% as a starting material, and mixed and mixed with polyvinyl alcohol (PVA) 5
Add 5 wt% of wt% aqueous solution and granulate 1
The average particle size is 5
A 0 μm Ni—Zn—Cu-based soft ferrite main fired powder was prepared. As a result of X-ray analysis of this powder, a sharp spinel structure diffraction line peculiar to soft ferrite was obtained, and it was confirmed that the powder was an extremely field crystalline magnetic powder. Next, the softening point (Td) 3 of the highly crystalline ferrite magnetic powder
3 wt% of alkali-free lead borosilicate glass powder having an average particle diameter of 1 μm at 80 ° C. was added and mixed, and then granulated.

Next, since the lateral groove and the vertical groove for winding the coil are formed by molding on the surfaces where the outer core and the inner core face each other, in the case of molding the outer core, as shown in FIG.
~ According to the manufacturing method shown in Fig. 10, a desired amount of granulated powder is uniformly filled in the mold as shown in Fig. 6, and the main mold is formed at a pressure of 3 ton / cm ² to form lateral grooves and vertical grooves. A cylindrical molded body 13 for the outer core was obtained.

In the case of the inner core, since a lateral groove is formed on the outer peripheral surface, a front sectional view of the inner core molding die of FIG.
As shown in the plan sectional view of FIG.
A desired amount of the above-mentioned granulated powder is filled in each split mold 23, and the upper pressing mold 24 and the lower pressing mold ² are pressed at a pressure of 3 ton / cm ² as described above.
Then, a cylindrical shaped body 28 for the inner core having the lateral groove 26 for the coil, the lateral groove 27 for the short ring, and the vertical groove was produced by press molding.

Next, these molded bodies 13 and 28 were individually placed in an electric furnace and heat-treated in air at 1200 ° C. for 60 minutes to obtain glass-bonded outer cores and inner cores. Then, wind a coil and a short ring around them,
A rotary transformer was produced by combining these.
At this time, as shown in the perspective view of the coil winding state of FIG. 14, since the slit-shaped convex portions 31 corresponding to the pitch of the coil 30 are formed at the groove bottom of the lateral groove 29, the coil 30 is wound at the time of winding. There was no detachment or floating, and more aligned winding was made with good yield. The measurement results of the material properties and the like of Example 1 are shown in (Table 1).

[0025]

[Table 1]

In Example 1, the shrinkage of the outer core and the inner core was 0.1% or less, and there was almost no shrinkage of the core due to the heat treatment, so that the mold dimension was obtained. With the gap of 70 μm or less, a highly accurate cylindrical rotary transformer can be realized, and a magnetic characteristic and a transformer characteristic are excellent.

(Embodiment 2) 3 wt% of the same glass powder and 5 wt% of epoxy powder as a resin were added to the same ferrite main calcination used in Embodiment 1 and mixed, and then the softening temperature of the resin was 90 or higher. After heat kneading at ℃ for 2 minutes, crushing and granulating this, the desired amount of this granulated powder was filled in the same mold as in Example 1, and the mold temperature was 180 ° C. for 30 seconds at 1 to
Compression molding was carried out at n / cm ² to produce outer and inner cylindrical molded bodies, respectively.

Next, these molded bodies were individually placed in an electric furnace, and after undergoing a degreasing process, they were heat-treated in air at 1200 ° C. for 60 minutes to obtain glass-bonding type ferrite cores for cylindrical rotary transformers. .. Then, as in Example 1, a coil and a short ring were wound around these lateral grooves, and these were combined to produce a rotary transformer.

Also in this case, the yield at the time of winding was very high. The measurement results of the material properties and the like of Example 2 are shown in (Table 1). In Example 2, the shrinkage ratio of the core was 0.
1% or less, core shrinkage due to almost no heat treatment is obtained, so that the size of the mold can be obtained, the gap between the outer core and the inner core is 70 μm or less, and a highly accurate cylindrical rotary transformer can be realized. Excellent characteristics and transformer characteristics were obtained.

(Example 3) The same ferrite powder used in Example 1 was added with 10 wt% of the same glass powder and mixed, and then granulated with an aqueous PVA solution. Next, this granulated powder is uniformly filled in a desired amount in the same mold made of stellite by the same method as in Example 2. At this time, a heater is attached to the outer periphery of the outer mold and the temperature is 150 ° C. for 1 minute for 1 to
Molding was performed by compressing the vertical pressing die with a pressure of n / cm ² to soften and melt the glass powder interposed between the magnetic powders. After the molding is completed, the mold is cooled to form the molded body in Example 2.
It was taken out in the same manner as in (1) to produce outer and inner cylindrical shaped bodies, respectively.

Next, these molded bodies were individually placed in an electric furnace, and heat-treated in air at 1200 ° C. for 60 minutes to obtain glass-bonded outer cores and inner cores.
A rotary transformer was produced in the same manner as in. Also in this case, the yield at the time of winding was very high. The measurement results of the material properties and the like of Example 3 are shown in (Table 1).

In Example 3, since the core shrinkage rate is 1% and the core shrinkage due to the heat treatment is small, a mold size close to that of the mold is obtained, and the gap between the outer core and the inner core is extremely high, 70 μm or less. It was possible to realize a cylindrical rotary transformer with high accuracy, and it was also possible to obtain excellent magnetic and transformer characteristics.

(Comparative Example 1) A mixture of starting materials having the same composition as in Example 1 was added with 5 w of a 5 wt% PVA aqueous solution.
After adding t%, the granulated powder is calcined at 1000 ° C. for 2 hours, finely pulverized to 2 to 5 μm, and the granulated powder is filled in a desired amount in a cylindrical mold for molding, and 3 ton Pressure molding was carried out at a pressure of / cm ² to prepare cylindrical inner and outer core hollow molded bodies.

This molded product was placed in an electric furnace, and 1200
After inviting in the air at 3 ° C. for 3 hours, the temperature was lowered while being cooled to obtain a Ni—Zn—Cu-based ferrite sintered type cylindrical core. In order to make the obtained cylindrical core into a desired size, the entire peripheral surface and the coil groove were machined to produce an outer core and an inner core. Next, coil winding was performed on these cores.
As shown in (4), the coil was lifted at the corner of the groove bottom of the core and the winding yield was slightly low. The measurement results of the material properties and the like of Comparative Example 1 are shown in (Table 1).

[0035]

INDUSTRIAL APPLICABILITY As described above, the rotary transformer manufacturing method according to the present invention requires a manufacturing process because the groove formation of the conventional cylindrical core is made by molding, unlike the case where the core is obtained by machining. Very easy,
The processing cost can be significantly reduced, and the yield of windings can be dramatically improved, so that a rotary transformer much cheaper than the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an inner mold used in a molding step of a method for manufacturing a rotary transformer according to an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of a ridge of a lateral groove forming die used for the internal die.

[FIG. 3] Manufacturing process diagram of the rotary transformer

FIG. 4 is a perspective view of an inner mold used in the molding process.

FIG. 5 is a perspective view showing a state where the internal mold is incorporated in a downward pressing mold.

FIG. 6 is a perspective view showing a state in which magnetic powder is supplied to a molding die in which an outer shape die is incorporated into the inner shape die.

FIG. 7 is a partially cutaway perspective view showing a state where a cap is removed from the molding die after molding.

FIG. 8 is a partially cutaway perspective view showing a state in which a cutting die is incorporated in the molding die.

FIG. 9 is a partially cutaway perspective view showing a state in which a cutting die is incorporated in the molding die.

FIG. 10 is a partially cutaway perspective view showing a state where a molded body is taken out from the molding die.

FIG. 11 is a sectional view of a rotary transformer manufactured by the manufacturing method.

FIG. 12 is a front sectional view of a molding die for the inner core in the first embodiment of the present invention.

FIG. 13 is a front sectional view of the molding die.

FIG. 14 is a schematic diagram showing a coil winding state in a coil lateral groove according to the first embodiment of the present invention.

FIG. 15 is a manufacturing process diagram of a conventional rotary transformer.

FIG. 16 is a perspective view showing a warped state and a contracted state of a core due to firing of a conventional cylindrical molded body.

FIG. 17 is a schematic diagram showing a coil winding state in a coil lateral groove of a conventional core.

[Explanation of symbols]

 1 central axis 2 vertical groove forming piece 3 vertical groove forming mold 4 horizontal groove forming mold 4b ridge 4c slit groove 7 internal mold 8 bottom pressing mold 9 external mold 10 magnetic powder 12 top pressing mold 13 molded body 18 outer core 19 outer coil 20 inner core 21 inner coil 31 slit-shaped convex portion

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Fujii 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A plurality of ridges having a plurality of slit-shaped grooves on the peripheral surface are provided around a vertical groove forming die having a vertical groove forming piece protruding in a radial direction on at least a part of a central axis. A plurality of lateral groove forming dies provided on the surface are arranged and combined to form an inner die, and the outer periphery of the inner die is covered with a cylindrical outer die, and the outer die and the inner die are combined with each other. After filling a desired amount of magnetic powder between, and press-molding the magnetic powder by inserting a pressing mold between the inner mold and the outer mold, the lateral groove forming mold The molded body is extracted by moving it in the direction of the central axis, the molded body is subjected to high temperature treatment to form a cylindrical outer core, and the outer coil is incorporated in a lateral groove having a slit-shaped convex portion formed on the inner peripheral surface of the outer core. After that, a rotary transformer that incorporates an inner core with an inner coil formed in the lateral groove of the outer peripheral surface into this outer core Manufacturing method. 2. The production of a rotary transformer according to claim 1, wherein the magnetic powder is a mixture of highly crystalline ferrite magnetic powder which has been sufficiently ferritized by high temperature firing and at least one of glass powder and resin is added. Method. 3. The method for manufacturing a rotary transformer according to claim 2, wherein the compression molding is performed in a heating state in which glass powder or resin is melted.